The invention relates to an antifriction insert for switching devices and also for slide surfaces for movable frog points to support a tongue or point of a frog which is movable with respect to a firmly mounted stock rail, the antifriction insert being fixed on a base member, arranged to be stationary with respect to the stock rail and so as to extend at right angles relative to the web thereof, and comprising a plurality of antifriction bodies of self-lubricating material retained in a rectangular frame.
Such an antifriction insert is known from EP-A-232 726 and DE-GM 87 00 566.2, respectively.
The antifriction insert consists of a sheet metal frame with breakthroughs in which the antifriction bodies are placed. A tongue or movable point of a frog rests with its bottom surface on these antifriction bodies which project above the surface of the slide chair and sheet metal frame.
For assembly, the antifriction insert is pushed into the recess mentioned above.
The frame in which the antifriction insert is disposed is lifted at its front end by means of a tool and pulled out of the recess in order to be able to exchange an antifriction insert of such design upon wear or destruction.
An antifriction coating of plastics for rail switches is known from DE-AS 26 31 594 with which a tongue is movable back and forth, sliding with respect to a rail, on a switch chair coated with plastics, and the plastics antifriction coating is arranged in a recess of the switch chair in such manner that it projects above the surface of the switch chair. The slipping of the tongue on the surfaces of plastics strips guarantees the functional reliability of the switch since the strips always maintain their planar shape due to their free movability or extensibility in all directions and do not become warped upwardly.
Moreover, an antifriction plate of plastics for a rail switch with switch chair and sliding switch blade is known from DE-OS 34 06 726, wherein the tongue is displaceable, substantially in a horizontal plane, on the surface of the antifriction plate received by the switch chair and accommodates load forces which are substantially vertical or inclined with respect to the horizontal, through the antifriction plate. The antifriction plate of plastics in this case is carried on a surface extending substantially horizontally of the switch chair and is retained between the lateral limiting strips thereof.
DE-GM 19 18 253 shows a streetcar rail switch with a tongue which is displaceable on an antifriction insert carried by a bottom member which is fixed both to the travelling rail and the side rail. The antifriction insert is fixed at both sides in a dovetail guide. For this reason, it can be exchanged only by pushing-in in a longitudinal direction, and that requires the complete dismantling of the entire streetcar rail.
OE-PS 319 990 shows a frog with a movable point which slides on an antifriction plate. This antifriction plate must be lubricated at regular intervals. It cannot be taken from this publication how the antifriction plate is fastened at the frog.
DE-PS 438 513 shows a way of supporting switch blades in the case of streetcar rail switches wherein the foot of the tongue is broader than the flange groove. Insertion of the switch blade or tongue into the streetcar rail is permitted by the fact that a recess is provided at the head of the side rail, which allows the tongue to be inserted laterally and then tilted.
Antifriction inserts of the kind mentioned initially are parts that are subject to wear and must be replaced from time to time--even if they have a long service life. This exchange is quite expensive with all the known antifriction inserts. Also in the case of the dovetail guide according to DE-GM 27 247 the antifriction insert must be pulled or beaten out of the dovetail guide means for its full length, and in practice that is possible with great difficulty only after the antifriction insert has had a prolonged period of service in the track since contamination and perhaps also corrosion hardly permit any displacement of the antifriction insert in the dovetail guide means. The cramped space available with streetcar rail switches renders the disassembly and renewed installation particularly difficult and, in most cases, requires total dismantling of the switch.